Video signals that contain television content, movies and other program content have been encrypted in many ways because such signals can be easily transmitted and copied electronically. Content providers who create electronic video content frequently encrypt their products or the associated audio/video signals in order to discourage others from copying those signals. These copy protection methods have met with a certain amount of success in discouraging end users or unlawful copiers from copying copyrighted material.
One way video content has been copy protected is by encrypting or encoding the actual video content as it is saved to a specific media. For example, the data stored on DVDs is encrypted with the CSS algorithm before it is stored on a DVD. Then when the information is played back from the DVD, it is unencrypted by the DVD player with the CSS algorithm and sent via a cable to the video display or television monitor. Such encryption systems have generally been effective in those situations where an individual desires to copy the video data directly from the source material (e.g. DVD).
Unfortunately, source level encryption does not protect the data from being copied in the situation where the information has been decrypted and is then being sent directly across the cable to the video display. In this situation, a knowledgeable individual can tap into the video cable between the video player or source and the video display while the image is being sent in its clear format. In this situation, a cable tap or splitter can be used to copy the signal just before it arrives at the video display. Alternatively, a copying machine can act as the video display and can intercept the direct output. This type of copying system enables the copier to avoid copy protections and copy a clean signal with very inexpensive hardware.
Some analog scrambling systems have been developed for satellite transmissions and for video tape copy protection. For example, some satellite signal copy protection systems strip away the vertical and/or horizontal sync pulses prior to sending the signal. Such copy protection systems send a reference sync signal or pilot signal and the decryption unit can then generate the missing sync signals from the reference signal. Without these control signals, analog video displays or televisions are unable to determine when to trace each new line in the frame or when a new frame begins.
Video tape systems use a similar copy mechanism so that when a video tape is copied the sync pulses are difficult to copy or otherwise modify so that they are not able to be copied properly. This results in a fuzzy or scrambled final picture on a copied tape.
Regardless of what type of scrambling or protection system is used for a video signal, there are some central components of video protection systems. Video protection systems tend to include an encoder to scramble, encrypt, or modify the video signal in some way. A central broadcast system or signal source device is also part of a protection system for distributing the video signals. In addition, at least one descrambler is typically located at the point where the video signal will be used. For satellite television or cable television, a descrambler is most often located with the video display that will display the signal. Accordingly, the video signal is generally decrypted just before it is sent across the analog transmission line to the video display or the television monitor. This means that the video display does not know anything about the scrambled signal that is sent to the descrambler unit because the signal has been descrambled before it is ever sent to the analog video display.